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C#加密解密算法

編輯：關於C語言

/*************************字符串加密算法***********************/
public string EncryptString(string str)
{
   char[] Base64Code=new char[]{'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','0','1','2','3','4','5','6','7','8','9','+','/','='};
   byte empty=(byte)0;
   System.Collections.ArrayList byteMessage=new System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes(str));
   System.Text.StringBuilder outmessage;
   int messageLen=byteMessage.Count;
   int page=messageLen/3;
   int use=0;
   if((use=messageLen%3)>0)
   {
    for(int i=0;i<3-use;i++)
     byteMessage.Add(empty);
    page++;
   }
   outmessage=new System.Text.StringBuilder(page*4);
   for(int i=0;i<page;i++)
   {
    byte[] instr = new byte[3];
    instr[0]=(byte)byteMessage[i*3];
    instr[1]=(byte)byteMessage[i*3+1];
    instr[2]=(byte)byteMessage[i*3+2];
    int[] outstr=new int[4];
    outstr[0]=instr[0]>>2;

    outstr[1]=((instr[0]&0x03)<<4)^(instr[1]>>4);
    if(!instr[1].Equals(empty))
     outstr[2]=((instr[1]&0x0f)<<2)^(instr[2]>>6);
    else
     outstr[2]=64;
    if(!instr[2].Equals(empty))
     outstr[3]=(instr[2]&0x3f);
    else
     outstr[3]=64;
    outmessage.Append(Base64Code[outstr[0]]);
    outmessage.Append(Base64Code[outstr[1]]);
    outmessage.Append(Base64Code[outstr[2]]);
    outmessage.Append(Base64Code[outstr[3]]);
   }
   return outmessage.ToString();
}
/**************************************************字符串解密算法**************************************************/
public string DecryptString(string str)
              {
   if((str.Length%4)!=0)
   {
    throw new ArgumentException("不是正確的BASE64編碼，請檢查。","str");
   }
   if(!System.Text.RegularExpressions.Regex.IsMatch(str,"^[A-Z0-9/+=]*$",System.Text.RegularExpressions.RegexOptions.IgnoreCase))
   {
    throw new ArgumentException("包含不正確的BASE64編碼，請檢查。","str");
   }
   string Base64Code="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/=";
   int page=str.Length/4;
   System.Collections.ArrayList outMessage=new System.Collections.ArrayList(page*3);
   char[] message=str.ToCharArray();
   for(int i=0;i<page;i++)
   {
    byte[] instr=new byte[4];
    instr[0]=(byte)Base64Code.IndexOf(message[i*4]);
    instr[1]=(byte)Base64Code.IndexOf(message[i*4+1]);
    instr[2]=(byte)Base64Code.IndexOf(message[i*4+2]);
    instr[3]=(byte)Base64Code.IndexOf(message[i*4+3]);
    byte[] outstr=new byte[3];
    outstr[0]=(byte)((instr[0]<<2)^((instr[1]&0x30)>>4));
    if(instr[2]!=64)
    {
     outstr[1]=(byte)((instr[1]<<4)^((instr[2]&0x3c)>>2));
    }
    else
    {
     outstr[2]=0;
    }
    if(instr[3]!=64)
    {
     outstr[2]=(byte)((instr[2]<<6)^instr[3]);
    }
    else
    {
     outstr[2]=0;
    }
    outMessage.Add(outstr[0]);
    if(outstr[1]!=0)
     outMessage.Add(outstr[1]);
    if(outstr[2]!=0)
     outMessage.Add(outstr[2]);
   }
   byte[] outbyte=(byte[])outMessage.ToArray(Type.GetType("System.Byte"));
   return System.Text.Encoding.Default.GetString(outbyte);

}
文件的加密解密說明：

    在對文件進行加密解密時，先將文件的內容讀取到一個字符串變量中，然後對字符串加密，最後再把加密後的字符串寫入到文件中。